Potentiostat/galvanostat with digital interface

Abstract

A potentiostat/galvanostat employs a controller for providing digital control signals to a digital-to-analog converter (DAC) that generates an analog output signal in response to digital control signals. A high current driver produces a high current output in response to the analog output signal from the DAC. A high current monitor monitors the output from the high current driver to produce a feedback signal for the high current driver to control the current produced by the high current driver and to produce an output dependent on the current supplied from the high current driver for monitoring by the controller. A counter electrode contact for a counter electrode is connected with the output of the high current monitor. A working electrode contact for a working electrode is electrically connected with a fixed stable voltage potential to enable electrochemical analysis of material between the counter electrode and the working electrode. A low current driver produces a low current range output in response to an analog output signal from the DAC. A low current monitor monitors the working electrode contact to detect current at the working electrode contact to supply an output dependent on the current detected for monitoring by the controller and for providing a feedback signal to the low current driver in order to control the output of the low current driver to control current between the counter electrode contact and the working electrode contact.

What is claimed is: 
     
       1. An electrochemical instrument comprising:
 a. a controller for providing digital control signals; 
 b. a digital-to-analog converter (DAC) in electrical communication with the controller for generating an analog output signal in response to digital control signals from the controller; 
 c. a low current driver in electrical communication with the DAC to produce a low current range output in response to the analog output signal from the DAC; 
 d. a counter electrode contact for electrical communication with a counter electrode connectable in electrical communication with the output of the low current driver; 
 e. a working electrode contact for electrical communication with a working electrode for enabling electrochemical analysis of material between the counter electrode and the working electrode; 
 f. a low current monitor connectable in electrical communication with the working electrode contact for detecting current at the working electrode contact and for supplying an output dependent on the current detected at the working electrode contact for monitoring by the controller and for providing a feedback signal for the low current driver in order to control the output of the low current driver to control the current between the counter electrode contact and the working electrode contact, the low current monitor including
 i. a monitor amplifier having an input connectable in electrical communication with the working electrode contact and having an output, 
 ii. an array of feedback resistors connected between the output of the monitor amplifier and input on the monitor amplifier, and 
 iii. a monitor analog multiplexer in electrical communication with the controller for selecting at least one of the feedback resistors in the array for electrical connection between the output and input of the monitor amplifier to control the output of the monitor amplifier. 
 
 
     
     
       2. The instrument of  claim 1  including a reference electrode contact for electrical communication with a reference electrode for positioning relative to the working electrode and the counter electrode in communication with the material, and a buffer for electrical communication with the reference electrode contact for detecting voltage at the reference electrode contact and for supplying an output dependent on the voltage at the reference electrode contact buffered from the reference electrode contact for monitoring by the controller and for providing a feedback signal for the low current driver to control the output produced by the low current driver to control the voltage at the reference electrode contact. 
     
     
       3. The instrument of  claim 2  including a feedback analog multiplexer in electrical communication with the controller and in electrical communication with the buffer for receiving the feedback signal from the buffer and the low current monitor for receiving the feedback signal from the low current monitor and for switchably selecting which of the feedback signals is output by the feedback analog multiplexer for the low current driver under the control of the controller. 
     
     
       4. The instrument of  claim 3  wherein the controller controls the feedback analog multiplexer to supply the feedback signal from the low current monitor to the low current driver when operating in low current mode and to supply the feedback signal from the buffer to the low current driver when operating in voltage mode. 
     
     
       5. The instrument of  claim 4  wherein the monitor amplifier includes a transimpedance amplifier having a gain dependent on the selection of a feedback resistor in the array for electrical connection with the monitor analog multiplexer. 
     
     
       6. The instrument of  claim 2  including an analog-to-digital converter (ADC) in electrical communication with the controller and in electrical communication with the outputs of the low current monitor and the buffer to convert the output signals of the low current monitor and the buffer to a digital signal for supply to the controller. 
     
     
       7. An electrochemical instrument comprising:
 a. a controller for producing digital control signals; 
 b. a digital-to-analog converter (DAC) in electrical communication with the controller for generating an analog output signal in response to digital control signals from the controller; 
 c. a high current driver in electrical communication with the DAC to produce a high current range output in response to the analog output signal from the DAC; 
 d. a high current monitor in electrical communication with the high current driver, the high current monitor producing a feedback signal for the high current driver in response to the current monitored by the high current monitor to control the current produced by the high current driver and for supplying an output dependent on the current supplied from the high current driver; 
 e. a counter electrode contact for electrical communication with a counter electrode and connectable in electrical communication with the output of the high current monitor; 
 f. a working electrode contact for electrical communication with a working electrode and electrically connectable with a fixed stable voltage potential for enabling electrochemical analysis of material between the counter electrode and the working electrode; 
 g. a low current driver in electrical communication with the DAC to produce a low current range output in response to the analog output signal from the DAC; and 
 h. a low current monitor connectable in electrical communication with the working electrode contact for detecting current at the working electrode contact and for supplying an output dependent on the current detected at the working electrode contact for monitoring by the controller and for providing a feedback signal for the low current driver in order to control the output of the low current driver to control the current between the counter electrode contact and the working electrode contact, the low current monitor including
 i. a monitor amplifier having an input connectable in electrical communication with the working electrode contact and having an output, 
 ii. an array of feedback resistors connected between the output of the monitor amplifier and input on the monitor amplifier, and 
 iii. a monitor analog multiplexer in electrical communication with the controller for selecting at least one of the feedback resistors in the array for electrical communication between the output and input of the monitor amplifier to control the output of the monitor amplifier. 
 
 
     
     
       8. The instrument of  claim 7  wherein the high current monitor includes a first high current range monitoring circuit for monitoring current in a first current range and a second high current monitoring circuit for monitoring current in a second current range. 
     
     
       9. The instrument of  claim 7  including a reference electrode contact for electrical communication with a reference electrode for positioning relative to the working electrode and the counter electrode in communication with the material and a buffer in electrical communication with the reference electrode contact for detecting voltage at the reference electrode contact and for supplying an output dependent on the voltage at the reference electrode contact buffered from the reference electrode contact for monitoring by the controller and for selectively providing a feedback signal for the high current driver to control the output produced by the high current driver to control the voltage at the reference electrode contact and for the low current driver to control the output produced by the low current driver to control the voltage at the reference electrode contact. 
     
     
       10. The instrument of  claim 9  including a high current switch for switchably connecting the high current driver in and out of electrical communication with the counter electrode contact and a low current switch for switchably connecting the low current driver in and out of electrical communication with the counter electrode contact, such that the controller controls the high current switch and the low current switch so that when the high current switch electrically connects the high current driver into electrical communication with the counter electrode contact the controller causes the low current switch to switch the low current driver out of electrical communication with the counter electrode contact. 
     
     
       11. The instrument of  claim 10  wherein the high current monitor includes a first high current range monitoring circuit for monitoring current in a first current range and a second high current monitoring circuit for monitoring current in a second current range and wherein the high current switch includes a first high current monitor switch for electrically connecting the first high current range monitoring circuit in and out of electrical communication with the counter electrode contact and a second high current monitoring switch for electrically connecting the second high current monitoring circuit in and out of electrical communication with the counter electrode contact. 
     
     
       12. The instrument of  claim 11  wherein the controller is in electrical communication with the first and second high current monitoring switches such that when one high current monitoring switch is turned on the other high current monitoring switch is turned off and when at least one of the high current monitoring switches is turned on the low current switch is turned off under the control of the controller. 
     
     
       13. The instrument of  claim 10  including a ground switch under the control of the controller for electrically connecting the working electrode contact in and out of electrical communication with ground when the high current driver is switched by the high current switch to be in electrical communication with the counter electrode contact. 
     
     
       14. The instrument of  claim 10  including a low current monitor switch under the control of the controller for switchably connecting the working electrode contact in and out of electrical communication with the low current monitor wherein the low current monitor switch electrically connects the working electrode into electrical communication with the low current monitor when the low current switch operates to connect the low current driver into electrical communication with the counter electrode contact. 
     
     
       15. The instrument of  claim 9  including a feedback analog multiplexer in electrical communication with the controller and in electrical communication with the high current monitor for receiving the feedback signal from the high current monitor, the buffer for receiving the feedback signal from the buffer, and the low current monitor for receiving the feedback signal from the low current monitor, and for switchably selecting which of the feedback signals is output by the feedback analog multiplexer under the control of the controller. 
     
     
       16. The instrument of  claim 15  wherein the controller controls the feedback analog multiplexer to supply the feedback signal from the high current monitor for the high current driver when operating in high current mode and to supply the feedback signal from the low current monitor to the low current driver when operating in low current mode and to supply the feedback signal from the buffer to at least one of the high current driver or the low current driver when operating in voltage mode. 
     
     
       17. The instrument of  claim 15  wherein the high current monitor includes a first high current range monitoring circuit for monitoring current in a first current range and a second high current monitoring circuit for monitoring current in a second current range wherein the first high current range monitoring circuit provides a first high current feedback signal for the feedback analog multiplexer and the second high current monitoring circuit supplies a second high current feedback signal for the feedback analog multiplexer, and when operating in the high current mode the feedback analog multiplexer under control of the controller selectively supplies the first high current feedback signal from the first high current range monitoring circuit for the high current driver when operating in the first current range and selectively supplies the second high current feedback signal from the second high current range monitoring circuit for the high current driver when operating in the second current range. 
     
     
       18. The instrument of  claim 17  wherein the first high current range monitoring circuit includes a first sense resistor connected in series between the high current driver and the counter electrode contact and a first instrument amplifier connected across the first sense resistor to detect the voltage produced by current flow through the first sense resistor to provide a first high current feedback signal and wherein the second high current range monitoring circuit includes a second sense resistor connected in series between the high current driver and the counter electrode and a second instrument amplifier connected across the second sense resistor to detect the voltage produced by the current flow through the second sense resistor to provide a second high current feedback signal. 
     
     
       19. The instrument of  claim 9  including an analog-to-digital converter (ADC) in electrical communication with the controller and in electrical communication with the outputs of the low current monitor, the buffer and the high current monitor to convert the output signals of the low current monitor, the buffer and the high current monitor to a digital signal for supply to the controller.